Cops didnt have FLIRS in 71 but military definitely did, I know that first hand. It was pretty classified back then. There were several kinds, real time thermal imagers for helicopters and COIN aircraft and line mapping recon systems carried by spy and recon planes. Those line mappers produced records that were looked at by ground based analysts, not pilots or crewmen. The real time FLIRS were extremely useful in combat and it was important to keep their capabilities secret.

Today, if you have about $7500, you can buy a FLIR, not a great one but a usable one. The military FLIRS were very sophisticated and used supercooled detector elements for enhanced thermal sensitivity and reduced noise. The civilian ones use uncooled detectors with much lower performance.

If Cooper used flares and there were FLIRS flying in the area while they were burning, he would have shown up, believe me. Even today chemical flares are fired as decoys by planes threatened by IR seeking missles. They are a great IR target.

The F 106s scrambled to chase NWA 305 had IRST gear, IRST=infrared search and track. It was useless for ground work and served only to alert the pilot to a hot jet exhaust in its field of view and allow him to track it. It did not present a video type picture.

Probably more than you or anyone on this forum ever wanted to know about thermal imaging.